A liquid crystalline TV has been developed for practical use which has a liquid crystalline display panel, the depth of the display panel is thin in comparison to a conventional display of a CRT. However, the liquid crystalline display panel does not radiate light itself, therefore, the image appearing on the panel is too dark to be recognized without the aid of some backlight to illuminate the image from rearside through the panel.
A flat luminescent lamp is disclosed in a published unexamined Japanese Utility Model Application SHO. No. 54-111985 and a published unexamined Japanese Patent Application SHO. No. 54-90877 as shown in FIGS. 15 and 16. These lamps consist of a lower glass panel 10 and upper glass panel 12 forming a vacuum cavity between them. Luminescent layers 22, 24 cover the inner surface of both panels, and a pair of electrodes 15 of hot cathode type is positioned in the cavity.
However, these lamps were developed for the use of lighting rooms and atmosphere not for the purpose of backlighting the liquid crystalline display panel. The shapes of the lamps are too narrow to be applied to the liquid crystalline TV display panel. Therefore, they cannot illuminate the TV display panel uniformly, also they are apt to produce uneven brightness for the image on the display panel even if they are used as a backlighting device for liquid crystalline display panel.
Furthermore, since they are driven with an alternative current being applied with alternating voltage to the electrodes 15, a noise caused by the alternating electric current and noise caused by plasma radiation at the electrodes enter the TV electric circuits to disturbe the TV image on the display panel.
The applicants of the present invention have previously developed a flat luminescent lamp which is disclosed in the published unexamined Patent Application SHO. No. 60-189154. The lamp is shown in FIG. 17 which consists of a lower glass panel 10 having an elevated margin at its entire periphery and spacing walls 40 extending longitudinally on its inner surface, an upper glass panel 12 forming a cavity between the lower glass panel 10 and a pair of electrode plates 14, 14 of the cold cathode type opposingly positioned in the cavity.
Luminescent layers are provided on the inner surface of both panels. The flat luminescent lamp in FIG. 17 can be used to backlight the liquid crystalline TV display panel but it was found still unfit for the liquid crystalline TV because of its uneven luminescent brightness to the display panel since the electrode plates 14, 14 emit most of electrons from a central portion of the electrode plates 14 and fewer from its sides.
Another problem of the flat luminescent lamp is that it is an inconvenient structure to be installed to or to be detached from the liquid crystalline display panel because each electrode plate 14 projects its lead plate 34 in the opposite direction from the under glass panel 10, therefore, a plug to provide access to the lead plate 14 ought to be provided at both longitudinal sides of the lamp which requires more space in the device of the liquid crystalline TV display.